Copyright WWW.DBBP.COM | updated 22 May-2007

My BMW Bobber, part 53
CAD version here


I took the completed wooden mold to Helmond, where two very talented metalshapers live. Ben (from Bens Metalshaping Shop) and Emile (from Barts Metalshaping) had offered to show us some metalshaping tricks. These two are real craftsmen and I am very gratefull that I was given this opportunity! The first step was to cover the wooden mold with a layer of ordinary masking tape.We decided it would be best to make the cover out of 3 pieces, and the edges of the 3 pieces were marked with red tape.


The next step was to cover the whole thing with glassfiber reinforced tape; this tape does not stretch so it will hold the shape of the pattern perfectly. On top of this layer we made some markings with a permanent marker so that the pattern pieces could be aligned perfectly at a later stage. Finally a second layer of reinforced tape was applied crosswise to the first layer. Now we had an exact pattern of the shape we wanted to make, we carefully peeled it off the wooden mold and covered the sticky side with talcum powder so it was not sticky anymore.


The 3 pieces of the pattern were carefully cut out, and we started with the top part. Using a radius template we determined the "crown" of the part, and used a matching tool in Emile's homemade Yoder. The Yoder uses a metal tool to hit the aluminum part, while the part rests on a rubber block. Sort of a mechanical version of the hammer and bag, working at a few hundred rpm to stretch the metal.


The lumpy surface that the Yoder makes is smoothed by a planishing hammer (also homemade). The planishing hammer flattens the metal between two steel tools at much higher rpm and leaves a smooth shiny surface. During the whole process the tape pattern is used to see where and how the metal needs to be shaped, when the pattern lies on the metal and touches it everywhere the part is finished. The cover is already finished but the story is getting too long for one episode, so it will be continued next week.